Particularly in the recent inkjet recording mediums widely distributed in the market, various technical approaches and proposals have been disclosed for the purpose of improving color developability and image fastness property at least to the same level as those of silver halide photography. Of them, there are many proposals for improving the image fastness property of recorded images by making metal ions and metal salts co-existent in addition to an ink-receiving material in an ink-receiving layer.
For example, Japanese Patent Application Laid-Open No. 2000-177235 discloses a recording sheet, in which a water-soluble metal salt or a hardly-soluble metal compound is simply added to an ink-receiving layer containing alumina hydrate in order to ensure gas resistance, light resistance, high ink absorbency, high ink fixability, high optical density and others of a recorded image. Furthermore, Japanese Patent Application Laid-Open No. S61-057380 discloses a recording sheet containing a porous inorganic pigment, a cationic resin and a magnesium compound having a water solubility of 1% or less at normal temperature in order to ensure water resistance, light resistance and high optical density.
Furthermore, as a recording medium using silica as an ink-receiving material, a recording medium using silica whose surface is treated with a compound or salt of monovalent or more metal ion has been proposed in order to improve the image fastness property of a recording image. Japanese Patent Application Laid-Open No. S63-166586 discloses a recording material containing silica whose surface is treated with a metal soap, a hydroxide, a salt and an oxide of a metal in order to improve color developability, light resistance and water resistance. This patent document discloses a method of treating the surface of silica, for example, by adding a metal salt during synthesis of silica under heating conditions of 90° C. and aging for 20 minutes. In short, timing of adding a metal compound for the surface treatment is disclosed. Furthermore, Japanese Patent Application Laid-Open No. H01-259982 proposes an inkjet recording sheet using silica whose surface is treated with calcium, magnesium and/or barium in order to improve light resistance. This document discloses, as a method of treating the surface of silica, a method of adding a metal salt to an aqueous solution having silica dispersed therein and heating the solution to 90° C. Furthermore, Japanese Patent Application Laid-Open No. H10-329404 proposes an inkjet recording medium containing a mixture of a porous aluminum oxide and a compound having a rare-earth metal series element of the periodical system and having an atomic number of 57 to 71 in an ink-receiving layer. The patent document discloses, as a method of treating the surface of a porous aluminum oxide, a method of adding a metal salt to an aqueous solution having the porous aluminum oxide dispersed therein and heating to 90° C.